SINGAPORE -- Singapore authorities have arrested 21 people on suspicion most of them belong to an al-Qaida-linked militant group that was plotting to blow up the U.S. Embassy, the government said Monday.

All the suspects were Singaporean citizens, the Ministry of Home Affairs said without releasing details of their arrests last month. None of them have been charged with any crimes, although they remain detained as allowed by the Internal Security Act.

The ministry said 19 of the suspects belong to Jemaah Islamiyah, a hardline Islamic group that authorities here say has cells throughout southeast Asia -- a region regarded as a second front in the global war on terror.

That fact was highlighted last week when U.S. embassies in Cambodia, Indonesia, Malaysia and Vietnam shut down because of security threats preceding the first anniversary of the Sept. 11, 2001, terror attacks in the U.S.

"These latest arrests have seriously disrupted the Jemaah Islamiyah network in Singapore," the ministry statement said. "There is no known imminent security threat from other Jemaah Islamiyah elements in Singapore."

Singapore has urged Indonesia to arrest Jemaah Islamiyah's alleged leader, Indonesian cleric Abu Bakar Bashir, but officials say they have no evidence against him.

Bashir denies any illegal activity.

The Singaporean government said some of the 21 suspects received military training at al-Qaida camps in Afghanistan and with the Moro Islamic Liberation Front in the southern Philippines.